An I_T nexus is a pairing of an initiator device and a target device. The devices that request input/output (I/O) operations are referred to as initiators and the devices that perform these operations are referred to as targets. For example, a host computer may be an initiator, and a storage array may be a target. The target may include one or more separate storage devices.
A Host Bus Adapter (HBA) is a hardware device that “connects” the operating system of a host computer and a communication path (e.g., a Small Computer System Interface (SCSI) (American National Standards Institute (ANSI) SCSI Controller Commands-2 (SCC-2) NCITS.318:1998) bus). The HBA manages the transfer of data between the host computer and the communication path.
Internet Small Computer Systems Interface (iSCSI) is a protocol (IETF RFC 3347, published February 2003; IETF Draft, published Jan. 19, 2003) that defines a technique for transporting SCSI commands/data to and from I/O devices across TCP (“Transmission Control Protocol”)-enabled networks (Internet Engineering Task Force (IETF) Request for Comments (RFC) 793, published September 1981). As such, iSCSI acts as a bridge between two independently designed protocols that have significantly different tolerances for, and facilities for, detecting and recovering from network congestion and from errors. iSCSI permits the existence of multiple parallel data paths to the same storage target.
HBA teaming refers to grouping together several HBAs to form a “team,” where each HBA in a team is connected to a particular target and may route data to that target. HBA teams may be built on an Internet Small Computer System Interface (iSCSI) portal group concept. A portal group concept may be described as a collection of network portals within an iSCSI Network Entity that collectively support the capability of coordinating a session with connections spanning these portals. HBA teaming may be used with Small Computer System Interface (SCSI) initiators running a Linux® operating system.
Notwithstanding conventional techniques for load balancing and failover, there is a need in the art for improved failover and load balancing across several HBAs, each of which may have one or more connections to the same target.